Active matrix substrates that are used for liquid crystal display devices and the like include a switching element for each pixel, e.g., a thin film transistor (hereinafter, “TFT”). As such switching elements, TFTs whose active layers are an amorphous silicon film and TFTs whose active layers are a polycrystalline silicon film have been widely used. In recent years, TFTs in which an oxide semiconductor is used instead of a silicon semiconductor have also been realized. Such TFTs are referred to as “oxide semiconductor TFTs”.
Now, an active matrix substrate has various circuits formed thereon, including semiconductor elements (which typically are TFTs). Circuits for protecting the semiconductor elements from ESD (electrostatic discharge; Electro-Static Discharge) are often provided. Such circuits are called ESD protection circuits, and function to prevent destruction of semiconductor elements due to electrostatic discharge.
An ESD protection circuit may be provided in the peripheral region (frame region) of the active matrix substrate, and includes, for example, two thin film diodes of different polarities connected to a gate line and a source line. These thin film diodes are connected to a reference potential line, for example. By using these, a charge which is accumulated in the gate line or source line can be released to the reference potential line.
However, introducing a conventional ESD protection circuit to a monolithic driver, for example, would lead to enlargement of the frame region of the display device. Therefore, Patent Document 1 discloses a technique which employs an ESD protection circuit of a simpler construction to allow the static electricity occurring in the substrate to be discharged at remote sites from semiconductor elements such as TFTs.
In the display device described in Patent Document 1, a portion (discharging portion) for promoting discharge is provided at the end portion of a scanning line (gate line). At this discharging portion, the end portion of a scanning line having a pointed shape and the end portion of a line also having a pointed shape oppose each other with a slight gap therebetween. The discharging portions are more liable to undergo a discharge than are other portions. Thus, by allowing ESD to primarily occur at the discharging portions, ESD occurrence at TFTs or other elements can be prevented.
Patent Document 2 describes a construction in which protruding electrodes are provided in the frame region in order to prevent destruction of elements or the like due to electrostatic discharge. Thus, providing a protruding electrode is likely to induce a discharge to occur at that site. As a result, discharge is restrained from occurring at other sites.